Oct 18, 2009

How to get Started

If you are interested in a normal fantasy world, you may not find anything useful in this post.  By "normal fantasy world," i mean one where the temperature, length of the year & the day are about the same as on Earth.  Often fantasy worlds have archaic or unique cosmologies, so that the nature of the sun, stars, moon, etc. are quite different from our own.  Somehow these cosmological differences seldom change the *effect* of the sun on the fictional world, but i suppose if you are re-writing the laws of physics, you can get any result you want.  I often find these fictional cosmologies quite interesting, but i won't digress further into these infinite possibilities.

Since i'm building a realistic sci-fi planet, & not assuming the sun & other features are just like earth’s, i need to find a good place to start.  A lot of the factors interrelated.  The only truly independent factor is the sun.  It will greatly effect your planet, but is not effected by it.

There’s a huge variety in the size of stars.  For “normal”, main sequence stars, the larger & brighter stars are bluer, while the smaller, dimmer stars tend to red. Wikipedia has a good overview of the star types.

Main sequence stars.  From Wikimedia.

Stars are often found together, orbiting their common center of mass.  “Binary”, or multiple stars & other exotic locations can be used for plausible sci-fi.  Niven even wrote about an inhabited ring of air orbiting a neutron star. But putting a habitable planet in one of these exotic settings require math beyond my power.  I leave them others’ imaginations.  This blog will focus on relatively earth-like worlds around a single main sequence star, which still leaves a huge number of variations.

But before you just pick your favorite color for a star, realize that the size & therefore color & brightness of a star is strongly connected to things like weather liquid water can exist, the temperature & length of the year. So how do you begin?

I offer three starting points:

The Easy, Automatic Starting Point

There are websites that can quickly create random, but reasonably realistic solar systems.  If you don't like the results you can press a button & get a new solar system in a few seconds.  Even if you want to be more hands on, you might find it useful to start with one of these generators & then tweak or redo the planet(s) by hand which you have a special interest in.

I recommend StarGen, which has a pretty easy to use interface, & allows you to specifically search for systems with habitable worlds, & gives you quite a bit of info on the planets.  It also makes some sophisticated calculations about temperature & atmosphere, & will tell you when planet should be tidally locked.

a StarGen screenshot

There's also the un-concisely named, An Applet for Synthesizing Solar Systems, a simpler, more straight-forward option, with less control & feedback.

There are additional solar system generators that run on Windows computers, for free and otherwise.  I haven't used them, since i use a Mac, so won't say anything about them.  I'll generally be sticking with free stuff, since i'm a cheapskate, though there are some apparently nice programs you could buy if you wanted to.

The Math-Lover’s, Do-It-Yourself Starting Point

You can find all the formulas you need at websites like Geoff's Creating an Earthlike Planet (with more explanations) or The World  Builder's Cookbook (with more equations).  You may find that you need to keep going back & changing variables to get rid of unexpected ramifications.  If that's true please see this post, where i provide the Celestial Architect spreadsheet that will do a lot of the calculations for you.  A spreadsheet is idea for slightly tweaking the variables to try to get the result you want.

The Way of Moderate Control & Effort

This one requires it own post.  The Celestial Architect will be my first chunk of usefully original content...

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